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The development of high-performance battery technologies necessitates ultrathin separators with superior mechanical strength and electrochemical properties. We present an innovative 1 µm thick, pinhole-free zeolitic imidazolate framework-8 (ZIF-8) layer, cathodically deposited on an 8 µm thick commercial polypropylene (PP) film in a rapid process, resulting in a ZIF-8@8-µm PP flexible membrane. This crack-free ZIF-8 layer, featuring angstrom-scale pores and chemical polar groups, functions as a Li+ sieve, regulating Li+ transport, controlling Li deposition, and blocking dissolved active cathode materials. It also enhances Li+ diffusion and transference number, extending the Sand’s time for Li dendrite formation. Consequently, the ZIF-8@8-µm PP separator addresses polysulfide shuttling in Li-S batteries and Li dendrite formation in Li-metal batteries, significantly improving their performance compared to conventional separators. Our findings indicate that while the 8-μm PP alone is unsuitable as a battery separator, the ZIF-8@8-μm PP, possesses the mechanical strength and electrochemical properties necessary for developing both Li-S and Li-metal batteries, as well as application in conventional Li-ion batteries with enhanced volumetric energy densities. 

Many transition-metal-oxide-based catalysts have been investigated to chemically bind soluble lithium polysulfides and accelerate their redox kinetics in lithium-sulfur (Li-S) battery chemistry. However, the intrinsic poor electrical conductivities of these oxides restrict their catalytic performance, consequently limiting the sulfur utilization and the rate performance of Li-S batteries. Herein, we report a freestanding electrocatalytic sulfur host consisting of hydrogen-treated VO2 nanoparticles (H-VO2) anchored on nitrogen-doped carbonized bacterial cellulose aerogels (N-CBC). The hydrogen treatment enables the formation and stabilization of the rutile VO2(R) phase with metallic conductivity at room temperature, significantly enhancing its catalytic capability compared to the as-synthesized insulative VO2(M) phase. Several measurements characterize the electrocatalytic performance of this unique H-VO2@N-CBC structure. In particular, the two kinetic barriers between S8, polysulfides, and Li2S are largely reduced by 28.2 and 43.3 kJ/mol, respectively. Accordingly, the Li-S battery performance, in terms of sulfur utilization and charge/discharge rate, is greatly improved. This work suggests an effective strategy to develop conductive catalysts based on a typical transition metal oxide (VO2) for Li-S batteries.